Over the last several years, accumulating evidence suggests that reversible acetylation may be a major regulatory mechanism for controlling protein function. Recent proteomic investigations have cataloged the existence of hundreds of acetylated proteins, implicating a potential regulatory role for nearly all facets of cellular biochemistry. Interestingly, metabolic enzymes constitute the largest portion of acetylated proteins. Only in a handful of examples has the functional significance of protein acetylation been revealed. Thus, there is tremendous need to determine the regulatory functions of protein acetylation, both at the level of physiological outcomes and at the level of molecular mechanism. This proposal directly investigates the central hypothesis that reversible acetylation is a major regulatory mechanism for controlling protein function. To accomplish these goals, we will investigate the biochemical and biological functions of sirtuins, NAD+dependent protein deacetylases, which are implicated in genome maintenance, metabolism, cell survival, and lifespan. The specific aims are focused on demonstrating a direct regulatory role for sirtuins in several major metabolic processes, and elucidating how site-specific acetylation affects enzyme function. Employing mechanistic enzymology, quantitative mass spectrometry, novel high-throughput assays, metabolic pathway analysis, structural biology, enzyme regulation, cell culture models, and mouse genetics, these studies will provide the first comprehensive understanding of the functional significance of reversible protein acetylation. The results have the potential to uncover the prominence of a previously-unknown regulatory mechanism and to transform how we understand metabolic and aged-related diseases.